Today is World UFO Day. People in different countries are coming together to share stories about alien encounters. Many will stay up late monitoring the sky for UFOs, but alien experts will remind people that the best evidence could be found hidden in ancient ruins on Earth, and at the bottom of old religious sites like Guatavita in Colombia.

The gold rituals at the circular mountain lake Guatavita, located just north of Bogotá, inspired the legend of El Dorado and other mysterious cities of gold. Ever since Spanish conquistadores in the 16th century witnessed an indigenous chieftain covered in gold dust dump precious metals into the lake, legends of vast wealth captivated future generations of fortune seekers. And while the lake continues to attract gold hunters who are keen on dredging Guatavita for sunken treasure, many people would be surprised by researchers who believe that the bottom of the lake also contains evidence of extraterrestrial life that came to Earth in search of gold.

Some have suggested that aliens used gold in their atmosphere to reflect the sun's rays and preserve their planet. But for those of you who are skeptical, and need scientific evidence to show why aliens would be so interested in gold, Derrick Pitts, Chief Astronomer and Planetarium Director for the Franklin Institute in Philadelphia, offers an explanation that describes gold as an important element for space exploration and astronomy.
"Gold is an inert material, it doesn't react with anything," he said in an interview for the popular History channel television series Ancient Aliens. "It is a wonderful conductor of electricity… and… a perfect reflector of infrared energy. You can use gold blankets to protect spacecraft against the intense heat of a star or any sort of heat source."

Others believe that aliens used ancient civilizations to mine for gold, and argue that if we examine old legends and temples we could identify patterns that prove the existence of extraterrestrial life. Following this argument, indigenous temples built over 1,000 years ago to commemorate the visitation of a god, and strange tribal chants and rituals that were designed to communicate with other worldly beings, could be interpreted as cultural evidence of alien contact.

One of the most famous alien visitations is supposed to have occurred in Cusco, Peru. The sun temple Qurikancha had a giant golden disc that some alien experts believe was a symbol of a gold-plated UFO that had landed in front of the Inca emperor Atahualpa, legendary for having direct contact with the "sky gods."

Other theorists go even further, claiming that the Great Pyramid of Giza is an ancient reactor that aliens used to make gold. But independently from whether you believe in aliens, ancient temples and mausoleums are like giant repositories for old sciences that have been lost. And these sciences can remind us that our ancestors were not only concerned with the environment and the planet, but also believed that survival was dependant on having a deep understanding of our solar system.

People have long looked up to the stars to figure out where they are, and where they will be going. So it is only natural that gold become a metaphor for our connection with the universe. Gold can remind us of the origin of our solar system. It is thought to have been made after the explosion of a star. The supernova scattered metallic dust that was later condensed into our solar system and the Earth. But sadly, gold can also remind us of our end. That we are at the early stages of an epic disaster where the sun could blow up or die out.

Aliens can similarly inspire us to tell stories about our future. They remind us that it is instinctual to dream about space. And they can become metaphors for the way that evolution pushes us to explore new places, and build new homes beyond Earth so that we can someday escape from extinction.

This is a popular theme in the new Superman movie Man of Steel, where Kryptonians have run out of resources and will need to flee from their planet to ensure survival. In this sense, the film presents aliens as an evolutionary force. However, this force can sometimes be polarized against humanity. General Zod, for instance, is a very cold and inhuman character, who determined to guarantee the survival of his alien race will sacrifice humanity without compassion.

Whether real or imagined, aliens challenge our beliefs and notions of what it means to be human. And while we are sometimes afraid of things that we don't understand, World UFO Day gives people an ideal to strive for, celebrate that we too are potential aliens. Someday we will venture beyond the limits of our solar system. And like Superman, the most famous alien in our culture, we hope to become symbols of our science and technology, and our compassion and morality.